The invention relates to a method for operating a preferably serial hydraulic hybrid drive system.
The Parker company has developed a serial hydraulic drive system, which is available under the name “RunWise”. It was developed for heavy commercial vehicles and is additionally retrospectively installed in a mechanical drive. In doing this the mechanical drive train is divided and the “RunWise” system is inserted.
All hybrid drive systems consist of energy converters, revolution rate converters and torque converters connected in series or parallel. Each of said converters, which are also referred to below as components, has operating point dependent efficiency, which usually depends on different external and internal influences.
The efficiency is defined here as the ratio of useful energy to energy expenditure:
                    η        =                              W            useful                                W            expenditure                                              (                  Eq          .                                          ⁢          1                )            
The operating point at which a component is operated has a significant influence on the efficiency of the component.
For each component the efficiency performance can be stored in the form of characteristic curves and/or characteristic fields.
A serial hydraulic drive train can e.g. comprise the following components: internal combustion engine, hydraulic pump, hydraulic motor and pressure reservoir. The components of the drive train can be operated in different operating modes. Thus the hydraulic motor can also be operated as a pump. When this is the case the hydraulic motor converts the kinetic energy of the vehicle into hydraulic energy and couples it into the pressure reservoir. Moreover, the pressure reservoir can be filled or discharged.
As a rule, the drive train has a different overall efficiency in different operating modes, even if it is providing the same useful power to the driven wheel(s) of the vehicle.